FAST002 fix is invalid with `...`

[CoderJoshDK]

Summary

FAST002 converts parameters into their Annotated counterparts. If the source code contains an ellipses type (literal ...) then the fix will generate incorrect semantics.

Take the following signature:

@router.get("/available")
async def get_available(
    ghl_account_id: str = Query(..., description="GHL account identifier"),
) -> SystemsAvailableResponse: ...

The use of ... in the default for Query is valid syntax (should be picked up in a lint that you shouldn't do this, but it is "valid").
When trying to run fix, you get:

@router.get("/available")
async def get_available(
    ghl_account_id: Annotated[str, Query(description="GHL account identifier")] = ...,
) -> SystemsAvailableResponse: ...

When in reality, there is no default value and ruff should convert it to:

@router.get("/available")
async def get_available(
    ghl_account_id: Annotated[str, Query(description="GHL account identifier")],
) -> SystemsAvailableResponse: ...

Version

ruff 0.14.0

[CoderJoshDK]

Minimum required repo:

uv add "fastapi[standard]"

# main.py
from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/")
async def root(name: str = Query(..., description="Your name!")):
    return {"message": f"Hello {name}"}

uv run fastapi dev main.py

If you then visit the docs page, you will find that "name" is marked as required. If you then run the fix:

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/")
async def root(name: Annotated[str, Query(description="Your name!")] = ...):
    return {"message": f"Hello {name}"}

And visit docs now; you find name is no longer required. Implying a default. But executing the endpoint will cause an error

ValueError: [TypeError("'ellipsis' object is not iterable"), TypeError('vars() argument must have __dict__ attribute')]

So I would consider this fix as incorrect, seeing that it changes the behavior. To match behavior after fix, drop the ....

[ntBre]

Thanks for the report, this does seem like a bug. At first I thought this was a general type error, but as you said, the ellipsis has special meaning to fastapi, and I think we should handle that in the fix.